Why is a cranking time specified for reciprocating compressors?
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I saw two separate instructions in different places; I need some guidance! The first theory is that if the cranking time is too short, the compressor completes only one rotation or too few rotations, which prevents any issues from becoming apparent; it also prevents a proper oil film from forming in the friction pairs before the motor starts. That’s why 5 minutes is specified as the appropriate cranking time. However, too long a cranking time is also not ideal, as the compressor’s speed is quite low during cranking, and it’s not possible to maintain an oil film at such low speeds for an extended period. If the amount of lubricant isn’t sufficient, dry friction may occur. Second theory: If possible, the device should run for 10–15 minutes per day with no load. Another method is to operate the oil pump driven by the auxiliary motor and the compressor cylinder lubricator for 10–15 minutes while manually turning the equipment, in order to ensure complete distribution of the lubricating oil.
We all do it in the first way
During normal standby, the crankcase oil system remains in operation; it pumps oil to lubricate the cylinders and the relevant adjustment components
There is some truth in each, it’s just that the focus is different.
Personal opinion: Generally, reciprocating compressors are lubricated with pressure oil. Before starting the cranking system, turn on the oil pump and the oil injector; wait until oil has entered before starting the cranking, and make use of the cranking system as much as possible. If turning the shaft manually, pay attention to controlling the speed of rotation. I personally disagree with the second opinion – starting a reciprocating compressor every day? Then I believe your failure rate will be relatively high. Since the moment of highest load on a reciprocating compressor is exactly when it starts up, don’t think it’s running at no load – the equipment has to overcome inertia while in operation, and at that instant the ammeter reading will spike dramatically.
There’s no need to follow such strict time limits for turning the engine over, right?
That’s indeed the case; there’s really no need to start the machine for a short period just to perform regular shaft rotation. With such a slow rotation speed, there’s no need to worry about dry friction. Dry friction occurs only during the moments of starting and stopping the machine. The lubrication pressure in piston compressors isn’t sufficient to lift the shaft off the ground. If you think about it carefully, you’ll understand: lol
I completely agree with you; if the equipment is in good condition, don’t start it casually unless necessary.